the fact of not being sexually loyal to your marriage partner or usual sexual partner

While he may have his faults, faithlessness isn't one of them. 虽然他有他的缺点，但不忠并不是其中之一。

She is cast in the role of the brilliant woman destroyed by her husband's faithlessness. 她扮演的角色是被丈夫的不忠摧毁的杰出女性。

the quality of not being loyal or able to be trusted

He was angered by the treachery and faithlessness within the movement. 他对这次运动中的背叛和不忠感到愤怒。

the state of having no religious faith

The present era is notable for unbelief and faithlessness. 现今世界无宗教信仰的人比比皆是。

She was an atheist shocked by the faithlessness of the believers. 作为无神论者，她对信教者信仰缺失感到震惊。